Projection television systems project enlarged cathode ray tube images upon remote screens. Color projection systems generally employ three picture tubes, one for each of the primary colors. In the conventional arrangement only one centrally located picture tube is aligned with the normal axis of the projection screen, and the other two are laterally displaced therefrom. This lateral displacement causes a number of problems, including color distortion.
The image light is horizontally distributed by vertical screen lenticules; and the brightness distribution varies as a function of horizontal viewing angle. Thus a viewer will see varying amounts of image light if he changes his seating location from side to center. Moreover these changes in image light levels are not identical for each of the three picture tubes because of their horizontal offset from each other. As the viewer changes his seating location the signal strength variations of the three tubes do not track each other.
Thus, different mixes of signal strengths are found at different viewing locations. Because each tube projects a different color, these different mixes are perceived as different color balances. Thus the lateral offset of the picture tubes causes the color balance to vary as a function of horizontal viewing angle. The present invention is directed at mitigating this change in color balance by rotating the peak values of the off-axis colors into a perpendicular attitude relative to the screen.
In copending patent application Ser. No. 222,836 entitled "Rear Projection Screen" and filed on Jan. 6, 1981 by the present inventor jointly with another, there is disclosed a procedure for developing the appropriate shape of a lenticule at any given screen location for compensating for image light reflection losses which vary as a function of the angle of incidence of the image light upon the lenticule. Since this angle of incidence varies as a function of screen location, in the copending patent application the lenticule profiles vary across the screen from center to edge.
In the present application a somewhat similar procedure is used as the first step in deriving the profile of a vertical lenticule. Thereafter the profile is revised and the final lenticule profile is then repeated horizontally across the screen. The resulting screen has novel light distribution properties, particularly with respect to the problem of horizontal color shift.